介孔SiO2/Fe3O4中空磁性微球的漆酶固定化

以介孔SiO2/Fe3O4磁性中空微球作为载体,采用物理吸附法对漆酶进行固定化,考察了时间、温度和pH值对漆酶固定化效果的影响,并对固定漆酶的活性及稳定性进行了研究.结果表明,介孔SiO2/Fe3O4磁性中空微球吸附漆酶分子后,介孔材料的比表面积与孔体积均减小.在3 h时复合微球对漆酶的吸附达到平衡,复合微球中介孔SiO2对漆酶的有效固定量为689 mg/g,大大高于纯介孔材料MCM-41的漆酶固定量(319 mg/g).在pH=3～6的条件下,复合微球中固定漆酶仍保持70%以上的相对酶活.当温度不高于60℃时,固定漆酶的相对酶活仍保持65%以上.固定漆酶的pH稳定性和热稳定性都明显优于游离漆酶,固定漆酶的米氏常数为1.05 mmol/L,与游离漆酶相比,固定漆酶与底物的亲和力有所降低.当2,4-二氯苯酚的浓度为10 mg/L时,固定漆酶对其去除率在6 h时达到81.6%,表现出很好的催化活性.     

Kinetics of adsorption of Saccharomyces cerevisiae mandelated dehydrogenase on magnetic Fe3O4–chitosan nanoparticles

The adsorption of Saccharomyces cerevisiae mandelated dehydrogenase (SCMD) protein on the surface-modified magnetic nanoparticles coated with chitosan was studied in a batch adsorption system. Functionalization of surface-modified magnetic particles was performed by the covalent binding of chitosan onto the surface of magnetic Fe₃O₄ nanoparticles. Characterization of these particles was carried out using FTIR spectra, transmission electron micrography (TEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Magnetic measurement revealed that the magnetic Fe₃O₄–chitosan nanoparticles were superparamagnetic and the saturation magnetization was about 37.3 emu g⁻¹. The adsorption capacities and rates of SCMD protein onto the magnetic Fe₃O₄–chitosan nanoparticles were evaluated. The adsorption capacity was influenced by pH, and it reached a maximum value around pH 8.0. The adsorption capacity increased with the increase in temperature. The adsorption isothermal data could be well interpreted by the Freundlich isotherm model. The kinetic experimental data properly correlated with the first-order kinetic model, which indicated that the reaction is the adsorption control step. The apparent adsorption activation energy was 27.62 kJ mol⁻¹ and the first-order constant for SCMD protein was 0.01254 min⁻¹ at 293 K.     

Facile synthesis of ordered magnetic mesoporous gamma-Fe2O3/SiO2 nanocomposites with diverse mesostructures

On the basis of a sol–gel process, a facile, low cost, and one-step approach for preparing ordered magnetic mesoporous γ-Fe₂O₃/SiO₂ nanocomposites by an evaporation-induced self-assembly (EISA) approach is presented. Various mesostructured silica materials (P6mm or Im3m) incorporated with different amounts of iron oxide (n_Si/n_Fe=9/1, 8/2, 7/3, respectively) were synthesized and characterized by XRD, TEM, N₂-sorption analyses, and superconducting quantum interference device (SQUID) magnetometer. The HCl-leaching experiments together with TEM micrographs and nitrogen sorption analysis suggested that most of the γ-Fe₂O₃ domains of several nanometers were embedded in the silica walls, rather than dispersed in the mesopores, which could cause the significant pore clogging reported in some studies. The release behaviors of lysozyme from these magnetic porous nanocomposites were investigated for the possible application of drug targeting and control release. The influence of iron precursors was also studied and a possible mechanism was proposed. The hydrolysis of Fe³⁺ ions under weakly acidic conditions and the induced formation of SiOFe bonds may account for the synthesis of this kind of nanocomposite. These multifunctional nanostructured materials would have a wide range of applications in toxin removal, catalysis, waste remediation, and biological separation as well as novel drug-carrier technologies.     

A highly selective magnetic sensor with functionalized Fe/Fe3O4 nanoparticles for detection of Pb2+

A magnetic sensor for detection of Pb~(2+) has been developed based on Fe/Fe_3O_4 nanoparticles modified by3-(3,4-dihydroxyphenyl)propionic acid(DHCA). The carboxyl groups of DHCA have a strong affinity to coordination behavior of Pb~(2+) thus inducing the transformation of Fe/Fe_3O_4 nanoparticles from a dispersed to an aggregated state with a corresponding decrease, then increase in transverse relaxation time(T_2) of the surrounding water protons. Upon addition of the different concentrations of Pb~(2+) to an aq. solution of DHCA functionalized Fe/Fe_3O_4 nanoparticles(DHCA-Fe/Fe_3O_4 NPs)([Fe] = 90 mmol/L), the change of T_2 values display a good linear relationship with the concentration of Pb~(2+) from 40 μmol/L to 100 μmol/L and from 130 μmol/L to 200 μmol/L, respectively. Owing to the especially strong interaction between DHCA and Pb~(2+), DHCA-Fe/Fe_3O_4 NPs exhibited a high selectivity over other metal ions.     

Reinvestigation of the Fe-rich part of the pseudo-binary system SrO–Fe2O3

The phase relations in the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃ (>33 mol% Fe₂O₃) were reinvestigated between 800 and 1500 °C in air. A combination of microscopy, electron probe micro-analysis, powder X-ray diffraction and thermal analysis was used to determine phase relations, crystal structure parameters and phase transition temperatures. M-type hexagonal ferrite SrFe₁₂O₁₉ (85.71 mol% Fe₂O₃) is stable up to 1410 °C. No indication of a significant phase width was found; Sr₄Fe₆O_13±δ appears as a second phase in compositions with <85.71±0.2 mol% Fe₂O₃. Sr₄Fe₆O_13±δ itself is stable between 800 and 1250 °C. Two other hexagonal ferrites were found to exist at high temperatures only: W-type SrFe²⁺₂Fe³⁺₁₆O₂₇ is stable between 1350 and 1440 °C and X-type ferrite Sr₂Fe²⁺₂Fe³⁺₂₈O₄₆ between 1350 and 1420 °C, respectively, which is shown here for the first time. These findings in combination with previously published data were used to derive a corrected phase diagram of the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃.     

Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

Chemoselective synthesis of δ-lactones via benzyl radical cyclization utilizing K2S2O8–CuCl2

Direct chemoselective oxidation of δ-lactones via highly stable benzyl radical cyclization is reported. The one-pot conversion of premade substituted 5-aryl pentanoic acid and 8-benzyl-1-naphthoic acid in the presence of K2S2Os--CuCl2 results to the δ-lactones in moderate to good yields. The advantages of this methodology is using water as a solvent and utilizing available starting materials.     

Fe_3O_4/RGO复合材料的制备及其电化学性能研究

以改进Hummers法合成的氧化石墨烯(GO)为前驱体,通过水热法结合烧结工艺制备了四氧化三铁/还原氧化石墨烯(Fe_3O_4/RGO)复合材料。利用X射线衍射(XRD)、拉曼光谱(Raman)、扫描电镜(SEM)、透射电镜(TEM)等手段对复合材料的理化性能进行表征;通过充放电测试、循环伏安(CV)和电化学阻抗谱(EIS)等技术,综合考察了材料的储锂性能及电化学性能增强机制。结果表明,在200和600 m A/g电流密度下,Fe_3O_4/RGO复合负极循环60次后的放电比容量分别保持在709和479 mAh/g,表现出良好的倍率性能;相较于纯Fe_3O_4负极,复合负极呈现出更优异的锂电性能,其电化学性能的改善得益于RGO能增强材料的电导性和结构稳定性。     

一种便捷方法制备表面氨基化的超顺磁Fe3O4纳米粒子

提出了一种简便易行的对磁性纳米粒子表面进行氨基化的方法. 首先使用化学共沉淀法合成了粒径为10 nm左右的Fe3O4纳米粒子, 然后用阿仑膦酸钠对其表面进行修饰, 使其表面具有了功能化的氨基. 利用透射电子显微镜(TEM)、X射线衍射(XRD)、振动样品磁强计(VSM)、动态光散射(DLS)仪、热重分析(TGA)仪、傅里叶变换红外(FT-IR)光谱仪、X射线光电子能谱(XPS)仪等对其进行表征. 结果显示磁性纳米粒子表面被成功地修饰了一层双膦酸分子. 所制备的纳米粒子可在pH=6.3稳定存在4周以上.     

Constructing magnetic polyaniline/metal hybrid nanostructures using polyaniline/Fe3O4 composite hollow spheres as supports

Polyaniline (PANI)/Fe₃O₄ composite hollow spheres have been successfully synthesized in one step using sulfonated polystyrene (PS) spheres as templates. The magnetic PANI hollow spheres were used as supports for noble metal nanoparticles (NPs) such as Au and Pd. The morphology, composition and magnetic properties of the resulting products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma (ICP) atomic spectra and vibrating sample magnetometer. The catalytic activity of magnetic PANI/Au composite shells on the oxidation of dopamine was investigated by cyclic voltammetry. The obtained results provide our product with a practical application for the detection of dopamine. On the other hand, the catalytic activity of magnetic PANI/Pd composite shells on the reduction of 4-nitroaniline was investigated by spectroscopic methods and compared with Pd/C catalyst which was already widely used in industrial production.     

Synthesis of pyranopyrazoles using magnetic Fe3O4 nanoparticles as efficient and reusable catalyst

Magnetic Fe₃O₄ nanoparticles as a heterogeneous catalyst, were found to be efficient for the synthesis of a series of pyranopyrazoles by a four component reaction of a mixture of hydrazine hydrate, ethyl acetoacetate, aldehydes/ketones and malononitrile in water at room temperature. The products were attributed to the nanosize of about 16 nm in which the catalyst could act as a nanoreactor. The present protocol offers the advantages of clean reaction, short reaction time, high yield, easy purification and economic availability of the catalyst.     

Preparation of “pore-fill” type Pd–YSZ–γ-Al2O3 composite membrane supported on α-Al2O3 tube for hydrogen separation

Mesoporous YSZ–γ-Al₂O₃ membranes were coated on α-Al₂O₃ (Ø2 mm) tube by dipping the α-Al₂O₃ support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al₂O₃ support. The quality of the mesoporous YSZ–γ-Al₂O₃ membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al₂O₃ content became more than 40%. Addition of γ-Al₂O₃ inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N₂ permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al₂O₃ layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al₂O₃ composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al₂O₃ layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H₂ flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al₂O₃ by elevation of temperature.     

Fast synthesis of dopamine-coated Fe3O4 nanoparticles through ligand-exchange method

A fast approach was described for the synthesis of water-dispersible monodisperse dopamine-coated Fe₃O₄ nanoparticles（DA-Fe₃O₄） with uniform size and shape via ligand-exchange of oleic acid on Fe₃O₄ using only 2 min.The prepared DA-Fe₃O₄ nanoparticles were characterized by transmission electron microscopy,Fourier transform infrared spectrometry,and vibrating sample magnetometer.The results indicated that the resulting DA-Fe₃O₄ nanoparticles had an average diameter of about 19.2 nm. The magnetic saturation value of the prepared DA-Fe₃O₄ nanoparticles was determined to be 72.87 emu/g,which indicating a well-established superparamagnetic property.     

Thermal transformation of quaternary compounds in NaF–CaF2–AlF3 system

Details of quaternary compounds formation in the system NaF–CaF₂–AlF₃ are specified. To achieve this aim, the samples of phases NaCaAlF₆ and Na₂Ca₃Al₂F₁₄ have been obtained by high-temperature solid-phase synthesis. Their thermal behavior when heated up to 800 °C has been studied using the methods of high-temperature X-ray diffraction (XRD) and thermal analysis (TA). The system under consideration can be regarded as a quasibinary section CaF₂–NaAlF₄, where at T=745–750 °C invariant equilibrium is implemented with the phases CaF₂–NaCaAlF₆–Na₂Ca₃Al₂F₁₄–(liquid melt)–(NaAlF₄). The peculiarity of the equilibrium is NaAlF₄ metastability at normal pressure. Below the equilibrium temperature the quaternary phase Na₂Ca₃Al₂F₁₄ is stable and NaCaAlF₆ above this temperature. The phase NaCaAlF₆ fixed by rapid quenching from high temperatures and when heated up to 640 °C decomposes, yielding Na₂Ca₃Al₂F₁₄. Further heating in vacuum at temperature up to 740 °C results in decomposition of Na₂Ca₃Al₂F₁₄ into CaF₂ and Na₃AlF₆. The expected reverse transformation of Na₂Ca₃Al₂F₁₄ into NaCaAlF₆ has not been observed under experimental conditions. Transformations in bulk samples reveal direct and reverse transformation of quaternary phases.

Synopsis

Thermal transformation of the quaternary compounds in system (NaF–CaF₂–AlF₃) was investigated using high-temperature X-ray diffraction (XRD) and thermal analysis (TA). In the system the invariant equilibrium is implemented with the phases CaF₂–NaCaAlF₆–Na₂Ca₃Al₂F₁₄–(liquid melt)–(NaAlF₄) at T=745–750 °C.     

Growth of single crystalline dendritic Li2SiO3 arrays from LiNO3 and mesoporous SiO2

A solution based wet chemistry approach has been developed for synthesizing Li₂SiO₃ using LiNO₃ and mesoporous silica as starting materials at 550 °C. A reaction path where NO and O₂ are formed as side-products is proposed. The crystals synthesized exhibit dendritic growth where the as-prepared nanodendrite is a typical 1-fold nanodendrite composed of one several microns long and some tenth of nanometers wide trunk with small branches, which are several hundreds of nanometers long and up to 70 nm in diameter. The effect of the structure of the mesoporous silica for the final morphology is discussed.     

Synthesis and characterization of novel magnetic Fe3O4/polyphosphazene nanofibers

Novel magnetic Fe₃O₄/polyphosphazene nanofibers were successfully prepared via a facile approach by ultrasonic irradiation. The structure and morphology were characterized by SEM, TEM, EDX, IR and XRD. The characterization results show that the magnetic Fe₃O₄/polyphosphazene nanofibers are several microns in length and 50–100 nm in diameter with Fe₃O₄ nanoparticles of 5–10 nm attached on the surface. The interaction between Fe₃O₄ nanoparticles and polyphosphazene nanofibers was thought as coordination behavior. TG curves show that the magnetic Fe₃O₄/polyphosphazene nanofibers have good thermostability and high magnetism content of about 44%. Magnetic studies show that the magnetic nanofibers exhibit good superparamagnetic properties with high magnetization saturation value of about 36 emu/g.     

Fe3O4/PEI/Au@CdSe/CdS多功能复合材料的制备与表征

以共沉淀法制备出Fe₃O₄纳米粒子,通过聚乙烯亚胺(PEI)修饰Fe₃O₄纳米粒子,再原位复合上Au纳米粒子,制得Fe₃O₄/PEI/Au纳米颗粒微球。再将Fe₃O₄/PEI/Au纳米颗粒与巯基乙酸修饰的量子点CdSe/CdS连接,成功制备了Fe₃O₄/PEI/Au@CdSe/CdS多功能复合微球。经过傅里叶变换红外光谱仪(FTIR)、荧光分光光度计、荧光显微镜、X射线衍射(XRD)、透射电子显微镜(TEM)及振动样品磁强计(VSM)的表征。结果表明:多功能复合微球的粒径在40nm左右,具有超顺磁性,剩磁,矫顽力近似等于零,饱和磁化强度为28.83A·m₂·kg^-1,同时兼有优越的荧光性能和金纳米粒子的特性。     

Fe3O4/PEI/Au@CdSe/CdS多功能复合材料的制备与表征

以共沉淀法制备出Fe₃O₄纳米粒子,通过聚乙烯亚胺(PEI)修饰Fe₃O₄纳米粒子,再原位复合上Au纳米粒子,制得Fe₃O₄/PEI/Au纳米颗粒微球。再将Fe₃O₄/PEI/Au纳米颗粒与巯基乙酸修饰的量子点CdSe/CdS连接,成功制备了Fe₃O₄/PEI/Au@CdSe/CdS多功能复合微球。经过傅里叶变换红外光谱仪(FTIR)、荧光分光光度计、荧光显微镜、X射线衍射(XRD)、透射电子显微镜(TEM)及振动样品磁强计(VSM)的表征。结果表明:多功能复合微球的粒径在40 nm左右,具有超顺磁性,剩磁,矫顽力近似等于零,饱和磁化强度为28.83 A·m²·kg^-1,同时兼有优越的荧光性能和金纳米粒子的特性。     

介孔SiO_2/Fe_3O_4中空磁性复合微球的制备与表征

采用多步包覆法在自制的240nm的单分散SiO2微球表面进行β-FeOOH的包覆,在5wt%的NaOH溶液中去除核心SiO2后,得到β-FeOOH纳米结构空心微球。将单分散的β-FeOOH空心球作为内核,十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,经水解缩聚反应得到空心核壳复合微球。在空气中焙烧(500℃,5h)对样品去除模板剂,并在还原气氛(5%H2/95%Ar,350℃,3h)下焙烧得到介孔SiO2/Fe3O4中空磁性复合微球。结果表明,所制得的介孔SiO2/Fe3O4中空磁性复合微球中的Fe3O4层厚度约60nm,是由Fe3O4纳米棒搭接而成的三维网络结构,复合微球的整体平均直径为390nm,比表面积较高约693m2·g-1,孔体积为0.63cm3·g-1,平均孔径为3.6nm,其饱和磁化强度可达13.6emu·g-1,同时较低的矫顽力(50Oe)有利于颗粒的再分散。     

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.